Japanese Industrial Standards JIS G 4313 standardizes 4 types of stainless steel strips for spring. They are austenitic SUS301-CSP, austenitic SUS304-CSP, martensitic SUS420J2-CSP and precipitation hardenable SUS631-CSP.
The austenitic stainless steel strips, SUS301-CSP and SUS304-CSP, are to be work hardened by cold rolling to increase strength, and depending upon the degree of the temper rolling (% rolling reduction) there are standardized 4 species of SUS301-CSP and three species of SUS304-CSP. Such austenitic stainless steel strips for spring are delivered in the cold rolled condition from a steel maker to a spring maker, where they are formed into desired shapes of springs, and thereafter when further enhancement of spring characteristics are desired they are subjected to aging of the order of 400.degree. C., 1 hour
The martensitic stainless steel strips, SUS420J2-CSP, are to be quenched and tempered to increase hardness (strength) thereby achieving spring characteristics. In many cases, such martensitic stainless steel for spring are delivered in the cold rolled and annealed condition from a steel maker to a spring maker, where they are formed into desired shapes of springs, and thereafter subjected to quenching and tempering treatment.
The precipitation hardenable stainless steel strips, SUS631-CSP, except for those of SUS631-CSP-0 which are delivered from a steel maker in the solution treated condition, are delivered in the cold rolled condition from a steel maker to a spring maker, as is the case with the austenitic strips, and by the spring maker they are formed into desired shapes of springs, and thereafter subjected to precipitation hardening to enhance spring characteristics. Incidentally, various precipitation hardenable stainless steel strips for spring, other than SUS631-CSP according to JIS, are commercially available.